Early ads of the HQ-100A
1. Overview of Modifications
The HQ-100A is fun to operate as is, but when I saw the updates in the HQ-200, I decided to add a product detector to it.
It was certainly an improvement.
Years later, I came across the AVC mod by WB6PUS. This made the radio more enjoyable.
Added a product detector by duplicating the circuit from the HQ-200. The HQ-200 is almost identical to the HQ-100A, except for its product detector.
A 6BE6 was installed in place of the 6BV8. A BAT46 diode was used as the AM detector and a 1N4148 for the noise limiter.
The BFO signal from 6BE6 was leaking back to the AM/AVC detector, causing a constantly high AVC voltage to develop.
This is not an issue, if the AVC is off when receiving SSB.
But I didn't like that, so a JFET based simple BFO circuit was added at the front panel BFO control, utilizing existing components.
This minimized the BFO leakage.
Added an external mute control. This is to mute the receiver when a transmitter is transmitting.
This achieves the same function as the SEND position.
It cuts the 105V regulated supply to the screen grids, the BFO and the prod detector. The 6C4 HFO is always on.
Modified the AVC for better SSB reception.
This mod was originally developed by Curtis (WB6PUS) for the HQ-160.
As an identical Z2 network is used in the HQ-100A, it was easy to adapt this for the HQ-100A. The AVC mode is switched automatically by a relay.